Insulating oils



INSULATING OILS James Campbell Wood-Mallock, Macclesfield, and Fred Hughes, Stretford, England, assignors to Manchester Oil Refinery (Holdings) Limited, Manchester, England No Drawing. Application March 28, 1955 Serial No. 497,391

Claims priority, application Great Britain March 30, 1954 2 Claims. (Cl. 252-63.7)

The present invention concerns improvements in insulating oils such as, for example, transformer oils, which are mineral oils used in transformers for cooling purposes, usually possessing a flash point over 160 C., having little or no volatility at 100 C. and free from moisture.

Transformer oil functions as a fluid di-electric medium and as a heat transfer fluid and in general any deterioration in the oil occurs slowly and progressively over a large number of years; "Deterioration occurs as a result 5 .of access of oxygento the system and contact of the oil insulant with the constructional materials of the transformer at the relatively high service temperature; Access of oxygen can be limited to some extent by the provision of conservators and the life of the oil insulant in such instances is usually long but in a number of cases and particularly with ventilated transformers severe failure occurs within a relatively short time.

It is known that of the materials normally used in the construction of a transformer the one which accelerates deterioration by oxidation to the greatest extent is copper. It has been shown that under certain conditions copper induces acidity development in the oil almost immediately so that the neutralisation number rises by 0.04 mg. KOH/ g. in the first ten days. Thus the conditions for solubilising copper in the insulating oil, namely, acidity and contact with the metal, do exist and although the rate of solution is extremely slow it is known that at low concentrations of a fraction of a part per million copper is extremely active and can catalyse oxidation. We have determined the copper content of a number of used transformer oil samples by the ion exchange technique described by H. Buchwald and L. G. Wood (Anal. Chem. 1953, 25, 664). It was found that copper was present to the extent of between 0.16 and 4 parts per million.

The use of anti-oxidants and metal de-activators in motor spirit has previously been proposed, but it has been found that no substantial benefits are obtained when the commercially available copper de-activators such as the tertiary organic amines Tenamene 60 (disalicylal propylene diamine in toluene) and Nonoxol CD (di-salicylal ethylene diamine), and many other proposed de-activators are added to transformer oil. Such additions cause an appreciable increase in the rate and amount of copper solubilised in most cases and do not result in any large reduction in sludge formation or acid development when the oil is subjected to the British Standard Specification 148-195 1 accelerated oxidation test, described in Insulating Oil for Transformers and Switchgear, published by British Standards Institution, 24-28 Victoria Street, London, S. W. 1, England, even when anti-oxidants are also present.

In contrast therewith, it has now been found that substantial benefits are obtained by the addition to transformer and other insulating oils of certain aromatic primary amines in combination with an anti-oxidant selected from the group consisting of phenyl-alpha-naphthylamine and phenyl-beta-naphthylamine.

, to the present invention.

The aromatic primary amines are those of the general formula wherein R R R and R are similar or dissimilar, are selected'from H and alkyl radicals containing up to 12 carbon atoms, and together do not contain more than 24 carbon atoms, and X is NH or COOH.

Examples of these aromatic amines are-orphenylene diamine, anthranilic acid and their nuclear substituted alkyl derivatives. The anti-oxidant may beeither phenyln-naphthylamine or phenyl-B-naphthylamine.

The preferred amount of metal deactivator present in i reduces the harmful effect of ,copper but also of other metals, e. g. iron, with Whichthe oil may come into contactduringuse. I

The ,solubilising effect onflcopper' of insulating oils treated according to the present invention andtheir. stability towards deterioration byoxidation have been assessed by tests simulating service conditions and by the B. S. 1484951 accelerated oxidation test'which'requires the use of a clean pure hydrocarbon (mineral) oil. The

results areiset out below together with comparative results for: the commercially available metaldeactivators Tenamenel;60, Nonoxol CD and Apc'olub'ef76i,

The test simulating service conditions in a ventilated transformer consisted in s ubjectinig 200 square centimetres of a copper surface, cleaned according to B. S. 148-1951, to the action of 200 millilitres of oil which is stirred at C. for three days in a thermostatically controlled bath and the amount of copper which dissolved in the insulating oil was determined by the method of Buchwald.

and Wood referred to above.

'In the tests the insulating oils used were transformer oil as currently marketed (B. S. 1481951), similar oil after being subjected to further treatments known in this art and transformer oil B. S. 1481951 treated according The additive P. B. N. referred to in the tables below is the anti-oxidant phenylp-naphthylamine. All percentages quoted are percentages by weight.

00 er Insulating Oil p iiiin,

' after 3 days at 70C.

a. B. S. 148-4951 Transformer Oil Batch Type A 1. 20 b. B. S. 148-1951 Transfu-rner Oil treated conventionally:

Type A after 3 x N N 21011 washes+3% activated earth. 0. 25 Type A after 3 x N N aOH washes, dehydrated 0.80 Type A distilled from solid N aOH 0.75 c. B. S. 1481951 Transformer Oil with Additives:

Type A+0.1% P. B. N I 0. 30 Type A+0.1% P. B. N.+0.02% Tenamene 60 3. 95 Type A+0.1% P. B. N.+0.02% Nonoxol CD 1.10 Type A+0.1% P. B. N .+0.02% ethylene diamine. 1.20 TypeA+0.1% P. B. N.+0.02% anthranilic acid 0 Type A+O.l% P. B. N .+0.02% o-phenylene diam 0 Type A+O.1 P. B. N.+0.0024% Accolube 76 3.

(Accolube 76 is a known deaetivator consisting of zinc hexyl dithiophosphate.)

Patented Jan. 13, .1959

and at least 0.02% t former 'oil B. 5. 1481951 will dissolve 1.2 parts per million of copper and that the conventional treating methods may reduce this to 025 part per million, whereas the addition of phenyl beta naphthylamirie as an antioxident and either anthranilic acid or o-phenylen'e diamine according to the invention prevents the solution of copper. The amount of copper dissolved when phenylbeta-naphthylamine and ethylene diamine are used according to the invention is identical With the amount dissolved in untreated oil. It has to be pointed out, however, thatthe method of analysis of Buchwald and Wood determines the total soluble copper whether present as a complex with a deactivator or as a copper soap of the acids developed when copper is contacted with insulating oil at elevated temperatures. I v

The results "obtained on carrying outth'e accelerated oxidation tests according to the method of B. S. 14l8--195 1 are given below:

Acid Development,

mg. KOH/g.

Sludge,

Insulating Oils Percent a. Base Oils: 7 V B. S. 148-1951 Transformer Oil Batch, Type B T pe B+0.02% ethylene diamine Type 13+0.o2% anthranllic acid Type B+0.1% P. B. N.+0.02% ethylene diamine Type B+0.1% P. B. N.+0.02% anthranilie am Type A'-|-0.1% P. B. N..

T %8 A+0.1% P. B. N.+0.02% Tenamene Type n+0.02% N onoxol CD Type A+0.1% P. B. N .+0.02% o-phenylene Cir It will be seen that the combination of phenyl-betanaphthylamine and the copper deactivators, anthranilic acid and o-phenylene diamine gave the best results in reducing sludge and acid development.

We claim: 7

1. A new insulating transfotmer oil composition consisting essentially of a mineral transformer oil and: (a) from about 0.001 to about 0.1% by Weight of a compound selected from the group consisting of anthranilic acid and o-phenylene diamine, (b) from about 0.01%. to

. about 0.25% by weight of a compound selected from the group consisting of phenyl alpha-naphthylamine and phenyl-beta-naphthylamin'e.

2. -A new insulating transformer oil composition consisting essentially of a mineral transformer oi'l',"and: (a) a compound selected from the group consisting of anthranili-c acid and o-phenylene dianiine in an amount effective to function as a metal deactivator in the transformer oil, and (b) a compound selected from the group consisting of phenyl-alpha-naphthylamine and phenyl-betanaphthylamine in an amount efiective to fuction as'an anti-oxidant in the transformer oil.

References Cited in the file of this patent 

2. A NEW INSULATING TRANSFORMER OIL COMPOSITION CONSISTING ESSENTIALLY OF A MINERAL TRANSFORMER OIL, AND: (A) A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ANTHRANILIC ACID AND O-PHENYLENE DIAMINE IN AN AMOUNT EFFECTIVE TO FUNCTION AS A METAL DEACTIVATOR IN THE TRANSFORMER OIL, AND (B) A COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHENYL-ALPHA-NAPHTHYLAMINE AND PHENYL-BETANAPHTHYLAMINE IN AN AMOUNT EFFECTIVE TO FUCTION AS AN ANTI-OXIDANT IN THE TRANSFORMER OIL. 